The South Ubangi Provincial Health Division in the DRC issued an alert for a suspected mpox case in January 2023 after the death of a fisherman displaying respiratory distress and skin lesions in Mbaya Health Zone. South Ubangi directly borders CAR, separated by the Ubangi River. The National Programme for Control of Mpox and Viral Hemorrhagic Fevers and the National Institute for Biomedical Research deployed a multidisciplinary team to investigate the case with the Provincial Health Division. As part of the investigation, the national and provincial health teams conducted supplemental training sessions to raise awareness of the clinical signs and transmission modes for mpox.

Figure 1

Figure 1. Possible transmission route of monkeypox virus between Bangui, Central African Republic, and Mbaya Health Zone, South Ubangi Province, Democratic Republic of the Congo, January 2023. Inset map shows location of...

The index case was an adult man residing in Bangui, CAR, who moved frequently between CAR and the DRC by the Ubangi River (cluster 1, case 1: C1) (Figure 1). After suspected exposure to wildlife meat and the potential consumption of rodents in CAR in early January 2023, symptom onset began shortly after (day 0); symptoms were fever, headache, chills, and cutaneous rash. After traveling to the DRC, he was admitted to Mbaya General Reference Hospital 2 days later, where he died on day 9 after symptom onset, after experiencing respiratory distress. No samples or information on his immune status were collected from this probable mpox case-patient.

We identified 15 contacts of the patient in Mbaya Health Zone, consisting of 5 healthcare workers and 10 close contacts (4 close friends and 6 family contacts). The investigation revealed a cluster of 3 symptomatic family contacts. Of those, 2 contacts had samples taken, and both tested positive for MPXV by PCR; those contacts were the adult female partner of C1 (C2) and their child (C3). A second child of C1 and C2 (C4) was treated locally for suspected mpox using traditional methods and was not investigated further. No suspected mpox cases were identified among family or close contacts of C1 in Bangui.

Figure 2

Figure 2. Possible transmission chain of monkeypox virus from CAR to the DRC and second identified chain at Mbaya General Reference Hospital, Mbaya, DRC. CAR, Central African Republic; DRC, Democratic Republic of...

Figure 3

Figure 3. Clinical manifestations of suspected mpox from 2 mother-child pairs in study of presumed transmission of monkeypox virus variants from Central African Republic to Democratic Republic of the Congo. One mother-child...

During the investigation, we identified a distinct second mpox cluster, which likely originated from a different source. We identified 3 suspected mpox cases in the same hospital at the same time as the first cluster that had no known epidemiologic link. An adult woman (cluster 2, case 1: D1) was hospitalized for nonspecific signs of mpox at the same time as C1 and reported contact with a child with mpox symptoms ≈28 days before. The 2 additional suspected cases were the child of D1 (D2), in whom mpox was subsequently confirmed by PCR, and a contact of D2 (D3), who tested negative by PCR (Figure 2). Confirmed mpox clinical symptoms included multiple pustular and papular lesions (C2); disseminated pustules (C3); discreet lacrimation in the left eye and postinflammatory hyperpigmentation (D1); and hyperpigmented, disseminated macules and steep-edged ulcerations (D2) (Figure 3).

Figure 4

Figure 4. Phylogenetic analysis of monkeypox virus (MPXV) sequences from Mbaya Health Zone in study of presumed transmission of MPXV variants from Central African Republic to Democratic Republic of the Congo. Phylogenetic...

We subsequently performed viral genome sequencing on 3 PCR-positive samples: 2 from the first mpox cluster (C2 and C3) and 1 from the second cluster (D2) (Figure 4). Phylogenetic analysis included 98 clade I MPXV previously published genomes. We generated the phylogenetic tree by maximum-likelihood using the Kimura 3-parameter model with unequal base frequencies plus gamma distribution plus invariable sites (12,13). The 3 sequences, all clade Ia, clustered with MPXV genome sequences isolated from CAR. The genetic distance between the new cases and the date between the CAR and DRC samples is too long to conclude direct links between the 2 countries. Nevertheless, the new samples from South-Ubangi clustered in the same subgroup (group II) according to previous classification of MPXV sequences in clade Ia (14).

Further, the National Programme for Control of Mpox and Viral Hemorrhagic Fevers investigated 109 suspected mpox cases from 15 health zones in South Ubangi during January–November 2023. Case-patients were predominantly male (60 male and 46 female; data were unavailable for 3 cases); the average age was 21 years (range 35 months–63 years). Of those, 61 cases (56%) were confirmed positive by PCR at National Institute for Biomedical Research. Three of the 46 mpox-negative cases (6%) were confirmed as positive for varicella zoster virus.

This investigation describes 2 distinct clusters of mpox cases in Mbaya Health Zone in South Ubangi Province in the DRC, presumably resulting from 2 different introductions. We identified epidemiologic links to cross-border travel from CAR for the first cluster and identified genomic links with historic CAR cases for both clusters. MPXV transmission in the DRC is currently driven by both zoonotic and human-to-human contact, thus increasing the complexity of containment and mitigation efforts. Wider regional and international expansion of mpox, specifically, the concentration of MPXV outbreaks in CAR and the DRC along the Ubangi River, recent sustained human-to-human transmission, resource limitations for identifying and treating mpox, disease stigma, population displacement because of conflict, and transient cross-border transit are serious concerns.

In August 2022, a first regional meeting involving 6 neighboring countries of Central and West Africa was held in Kinshasa, the DRC, to establish a regional mpox surveillance network, the Mpox Threat Reduction Network. Through this network, multiple teams including experts from the Health Ministries of the DRC and CAR were able to communicate rapidly on suspected cases crossing borders in South Ubangi while also reporting to International Health Regulations focal points. Considering the relatively porous borders in the Central African region and continuing increases in reported mpox cases, documenting transboundary mpox transmission is critical. This investigation highlights the importance of long-term collaborative partnerships for sustained mpox surveillance and containment in endemic regions.